Our study used two earthquake-modeling meth-
ods to assess seismic hazards and risks, and to
Deterministic: This method assumes the
location and magnitude of specified scenario earth-
quakes and determines the effects from these par-
Probabilistic: This method uses the informa-
tion from all historic earthquakes, plus geologically
inferred earthquake sources (faults, locations and
magnitudes), and computes the probable ground
shaking levels that may be experienced during, say,
a 100-year, 500-year or 2,500-year recurrence period.
These two methods complement one another.
Deterministic scenarios provide the “what if”
answers for particular assumed earthquakes. As we
change their magnitudes and locations, we can see
how various areas are differentially affected by differ-
ent events. However, for deterministic scenarios, we
do not ask how likely each scenarios is. The deter-
ministic scenarios are good for testing a region’s
emergency preparedness and how it would cope with
disaster losses of various magnitudes.
finds the long-
of shaking in
each area and,
a given area is
It tells how this
shaking for a
100-year, 500-year, or 2,500-year recurrence time.
These probabilistic estimates serve best for urban
planning, land-use, zoning, and seismic building code
regulations, but they also help to determine risk-
based earthquake insurance premiums.
Since this method is based on predetermined
scenario earthquakes, we chose the 1884 M5.2
historic earthquake, located off shore of Brooklyn,
represented by the star on the first map to the left.
However, instead of a single magnitude, we com-
pared the effects of three magnitudes – M5, M6
and M7 – in the surrounding region. Using HAZUS,
we were able to model the ground mot